It is of great significance to crack down on carriage and transportation of high atomic number matters, such as nuclear materials, nuclear weapons and radioactive dispersal devices. Since the 911 incident in the U.S., prevention and handling of nuclear and radioactive terrorist attacks have become a significant social security issue the countries all over the world have to face. Compared with other terrorist attacks, while terrorist attacks with crudely made nuclear devices happen at a relatively low probability, their consequences will be very severe, including not only massive casualties, but also damages to economic development and even panics and instabilities of the society. Hence, the surveillance on nuclear materials for producing nuclear devices has become a nuclear security issue the global society has paid great attention to.
Since the beginning of the 21st century, there have been hundreds of millions of containers transferred all over the world every year. Recently, the terrorism has become increasingly rampant and there are increasingly higher risks of nuclear and radioactive terrorist attacks. Terrorists may hide weapons of mass destruction or radioactive dispersal devices in containers carrying commercial goods for transportation to the destination of the attack. Hence, there is a need for inspecting whether there are any hidden nuclear materials, nuclear weapons or radioactive dispersal devices, so as to reduce security risks while ensuring fast and stable commercial transportations.